What part of speech is "онлайн" then? I'll give you that "сайт" is a technical loan-word, though I still can't come up with a situation where something.сайт would make sense. Of course it's a goddamn site, it's the Internet after all.

Saw it used as adjective and noun, with multiple meanings, akin to usage in english language. And I don't see much sense in '.сайт' too, but I don't see much of it in most new gTLDs.